For cultivation of cells, particularly eukaryotic cells, and more specifically mammalian cells, there is a constant need to use special culture media providing nutrient substances that are required for efficient growth of cells and for the production of biological products, especially biopharmaceuticals, such as, for example, recombinant proteins, antibodies, viruses, viral antigens, and virus-like particles. For the efficient production of said biological products, it is important to achieve an optimal cell density as well as an increase of the protein expression itself in order to obtain maximal product yield.
Cell culture media formulations have been supplemented with a range of additives, including undefined components like fetal calf serum (FCS), several animal derived proteins and/or protein hydrolysates of bovine origin as well as protein hydrolysates derived from plants or yeast.
In general, serum or serum-derived substances, such as, e.g., albumin, transferrin or insulin, may comprise unwanted agents that can contaminate the cell cultures and the biological products obtained thereof. Furthermore, human serum derived additives have to be tested for all known viruses, including hepatitis viruses and HIV which can be transmitted via serum. Moreover, bovine serum and products derived thereof bear the risk of BSE contamination. In addition, all serum-derived products can be contaminated by unknown substances. When using serum or protein additives derived from human or animal sources in cell culture, there are numerous problems (e.g., the varying quality in composition of different batches and the risk of contamination with mycoplasma, viruses or BSE), particularly if the cells are used in the manufacture of drugs or vaccines for human administration.
Therefore, many attempts have been made to provide efficient host systems and cultivation conditions, which do not require serum or other animal protein compounds.
Such serum-free media have been developed on the basis of protein extracts derived from plants or yeast. For example, soy hydrolysates are known to be useful for fermentation processes and can enhance the growth of many fastidious organisms, yeasts and fungi. WO 96/26266 describes that papaic digests of soy meal are a source of carbohydrate and nitrogen and many of the components can be used in tissue culture. Franek et al. (Biotechnology Progress (2000) 16, 688-692) describe growth and productivity promoting effects of defined soy and wheat hydrolysate peptide fractions.
WO 96/15231 discloses a serum-free medium composed of a synthetic minimal essential medium and a yeast extract for the propagation of vertebrate cells and a virus production process. A medium formulation composed of a basal cell culture medium comprising a rice peptide and an extract of yeast and an enzymatic digest thereof, and/or a plant lipid for growth of animal cells is disclosed in WO 98/15614. A medium comprising purified soy hydrolysate for the cultivation of recombinant cells is disclosed in WO 01/23527. WO 00/03000 discloses a medium that comprises a soy hydrolysate and a yeast extract, but also requires the presence of recombinant forms of animal proteins, such as growth factors.
EP-A-0 481 791 describes a biochemically defined culture medium for culturing engineered CHO cells, which is free from protein, lipid and carbohydrate isolated from an animal source, further comprising a recombinant insulin or insulin analogue, 1% to 0.025% w/v papain digested soy peptone and putrescine. WO 98/08934 describes a serum-free eukaryotic cell culture comprising hydrolyzed soy peptides (1-1000 mg/L), 0.01 to 1 mg/L putrescine and a variety of animal-derived components, including albumin, fetuin, various hormones and other proteins. In this context, it should be noted that putrescine is also known to be comprised in standard media like DMEM/Ham's F12 in a concentration of 0.08 mg/L.
The plant and/or yeast hydrolysates, however, are undefined mixtures of oligopeptides and other unknown components and contaminants. Moreover, the quality of commercially available lots of hydrolysates varies extremely. As a result, there are large variations in the production of recombinant proteins or viral products (a variation of up to a factor of 3) as a function of the lots of hydrolysates used (“lot-to-lot variation”). This drawback affects the proliferation of the cells as well as the protein expression of each cell.
In summary, the media known in the state of the art are supplemented with proteins or peptide extracts derived from animals, plants, or yeast; or with recombinant versions of proteins, such as, for example, insulin, insulin like growth factor or other growth factors.
Therefore, there is a need for a cell culture medium which is free of animal, herbal, and fungal proteins and/or oligopeptides in order to overcome the above-mentioned problems. Furthermore, a current need exists to increase the yield of expressed recombinant proteins or any other expression product, and to provide an optimal cell culture medium for the production of biological products, such as those used as pharmaceuticals or vaccines in humans.